The invention relates to a pressure swing adsorption process for the purification or separation of gaseous mixtures with the use of plural cyclically reversible adsorbers undergoing through substantially identical cycles.
Such a process is known, for example, from DAS No. 2,038,261. The process described therein, operating with four cyclically reversible adsorbers, comprises, following the single adsorption phase, four expansion phases, a desorption phase, and three pressure buildup phases. The desorption takes place by purging the adsorber with the gaseous mixture discharged during the second expansion phase. The final expansion phase gas is blown off as the purging gas enriched during the adsorbed gas with the desorbing components. The first and third expansion phases take place respectively in pressure equalization with other adsorbers which are then in their first or second pressure buildup phases, respectively. The second expansion phase takes place concurrently, based on the direction of gas flow during adsorption, the fourth and final expansion phase takes place countercurrently. The adsorption front is still within the adsorber packing at the end of the adsorption phase. Breakthrough of the adsorption front occurs at the earliest, after the two first expansion phases have run their course. The full loading of the adsorber filling accordingly occurs only at a pressure which is greatly reduced as compared to the adsorption pressure. The adsorption filling capacity of the components to be adsorbed is thus utilized only up to a certain degree, since the quantity of adsorbed components decreases as the pressure decreases. The object of this special mode of operation resides in obtaining a purging gas to enhance the desorption, which gas does not contain the components to be desorbed, and in the prior art exhibits the composition of the purified product gas. As a consequence, a considerable portion of the product gas to be obtained is lost by being blown off into the atmosphere, primarily during the desorption phase conducted with a purging stream, but also during the final expansion phase, since the expansion gas discharged still contains proportions of the product gas to be obtained.